1. Field of the Invention
This invention relates to a device for detecting a color of an ink carrier for use with a thermal transfer recording device.
2. Description of the Prior Art
In a thermal transfer recording device, an ink carrier to which thermally fusible or sublimable ink is applied, is contacted face to face at an ink layer thereof with record paper, and a thermal head is pressed against a face of the ink carrier opposite to the ink layer and is heated in accordance with a record pattern to transfer ink to the record paper to effect desired recording. This thermal transfer system is advantageous in that multi-color recording can be easily attained with an ink carrier to which at least three inks of different colors of yellow, magenta and cyan are sequentially and repeatedly applied. In this system, however, since the inks of the three colors are transferred one upon another to obtain a record and this is repeated for a required number of times, it is necessary to detect a color of ink in order to position the ink carrier to individual color positions for transport of the ink carrier.
A conventional ink carrier color detecting device of the type wherein an ink carrier having a construction as shown in FIG. 1 is used, is already known. Referring to FIG. 1, an ink carrier 1 carries thereon an ink layer 2 in which a set of inks of yellow Y, magenta M and cyan C are applied sequentially and repeatedly. In order to allow detection of a color of ink on the ink carrier 1, black band-formed marks are provided between adjacent ink areas of different colors of the ink layer 2. The marks 3 consist of a mark 3a extending over the entire width of the ink carrier 1 and located forwardly of each area of the first color, that is, yellow Y, which provides a reference for transfer of ink of the three colors, and marks 3b and 3c each extending over about two thirds of the width of the mark 3a and located forwardly of each, are of the second and third colors, that is, magenta M and cyan C, respectively. In the conventional device, a pair of optical detecting means are located adjacent opposite side edges of an ink carrier 1 and detect the length of each of the marks 3 in order to position a yellow Y ink area providing a reference for transfer when a mark having a length greater than the length of another mark for an ink area of magenta M or cyan C, that is, a mark for an ink area of yellow Y, is detected. Further, while yellow Y of the reference color is identified, magenta M and cyan C cannot be distinguished from each other from the marks 3b and 3c since the marks 3b and 3c for magenta M and cyan C are identical to each other, and hence the two colors are distinguished in accordance with the sequential order from the reference color. This device, however, has a drawback that if a detection error of a mark 3 should occur, a wrong color may possibly be selected for transfer, and therefore reliability of the device cannot be high. For example, if detection of a mark 3b for magenta M should fail, cyan C would be detected as the second color and hence transfer of cyan C would occur where transfer of magenta M must occur.
Another typical ink carrier color detecting device is disclosed in Japanese Laid-Open Patent No. 58-140266 and is constituted as illustrated in FIGS. 2 and 3. Referring to FIGS. 2 and 3, lamps 13 and phototransistors 14 are located adjacent opposite faces of an ink donor sheet 11 and in a line perpendicular to a plane of the ink donor sheet 11 with filters 12a, 12b and 12c corresponding to the colors of the inks interposed between the lamps 13 and the ink donor sheet 11. The collector of each of the phototransistors 14 is connected to an input of a comparator 16 via an amplifier 15. A predetermined fixed reference voltage is applied to the other input of the comparator 16 via a resistor 17. An output of the comparator 16 is inputted as a detected color signal to a logic circuit 18.
The comparator 16 is constructed to provide an output signal "1" when there is an input from the amplifier 15 depending upon a reference voltage thereto.
In this conventional device, three identical systems each including such a comparator 16 are provided, and for the three systems, the filters 12a, 12b and 12c of colors corresponding to the colors of the inks as well as the lamps 13 and the phototransistors 14 are arranged in juxtaposed relationship along a widthwise direction of the ink donor sheet 11. The filters include a red filter 12a, a green filter 12b and a blue filter 12c. FIG. 3 is a diagrammatic representation illustrating an arrangement of the colors on the ink donor sheet 11. The ink donor sheet 11 includes an ink carrier 11a in the form of a polyester film or the like, and ink 11b is applied in a widthwise direction to a surface of the ink carrier 11a. Here, the ink 11b is applied repeatedly in an order of yellow Y, magenta M, cyan C and black B.
The conventional ink donor sheet color detecting device is constructed as described above. Thus, in this device, making use of a characteristic that a portion of the ink donor sheet 11 of a particular color is not pervious to light of a color complementary to the particular color, light beams of three colors individually complementary to the colors of the ink donor sheet 11 are thrown onto the ink donor sheet 11 and light passing therethrough is detected to distinguish a color of the ink. For example, if the color of ink on a portion of the ink donor sheet 11 is cyan C, the lamp 13 for the circuit for which the red filter 12a are provided, emits red light which does not pass through the portion of the ink donor sheet 11 and hence the corresponding phototransistor 14 remains in an off condition so that the comparator 16 outputs a signal "0". Meanwhile, in the circuits for which the green filter 12b and the blue filter 12c are provided, the lamps 13 emit green light and blue light, respectively, which pass through the portion of the ink donor sheet 11 so that the corresponding phototransistors 14 are turned on. Outputs of the two phototransistors 14 are amplified by the amplifiers 15 connected thereto and are then inputted to the associated comparators 16 so that a signal "1" is outputted from each of the comparators 16. The output signals of the comparators 16 are inputted to the logic circuit 18, and the logic circuit 18 thus distinguishes depending upon the input signals thereto that the ink on the portion of the ink donor sheet 11 is now cyan C. As a result, a transfer device will select the color, cyan C, to thermally transfer the ink of the color onto a predetermined sheet of paper in accordance with a prescribed pattern.
However, the conventional device as described just above, requires three identical circuit systems and thus requires the individual elements from the lamp 13 to the comparator 16 for such three systems. Accordingly, the conventional device has a drawback that production costs are raised and a circuit construction therefor becomes complicated, resulting in deterioration in reliability of the device.